Magnetic chain conveyors comprising curved portions have been known for many years (see for example EP0286173 and EP0509605), the curved portions of said conveyors being generally formed in one piece and comprising cavities closed by covers in which the magnets are housed.
Alternatively, it is also known to form said curved elements by incorporating the magnets or magnetic material into their interior (see for example EP0336170).
The chains travel along the conveyor curved elements incorporating the magnets, resulting in deterioration of the slide surface of these elements with time. This problem is overcome by completely replacing the curved element, ie both the part along which the chains travel and the part housing the magnets. For reasons of simplicity and to reduce maintenance times, the deteriorated elements are generally replaced by new elements already incorporating the magnets. In this respect, the operations involved in removing the magnets from the deteriorated curved elements and inserting them into the new curved elements, should this be possible, woudl be relatively lengthy and difficult. However this maintenance procedure negatively affects maintenance costs, as the magnets represent a substantial part of the total element cost.
Embodiments are known (see EP0207577) in which the curved element is formed from several separate parts. These embodiments comprise a plurality of first separate parts on which the chain travels and a plurality of second separate parts in which the magnets are housed. Even with such elements, when the plurality of first parts on which the chain travels become worn the curved elements are completely replaced. In this respect, to replace only the parts on which the chain travels, the entire element consisting of as many as fourteen parts would have to be dismantled, this operation being relatively lengthy and difficult.
It is also known to construct at least that part of the conveyor which comes into contact with the chain from a high molecular weight polyethylene, for which it has been considered so far to use polyethylenes having a molecular weight of up to about 6 million g/molecule. To further improve the sliding resistance of the elements, ceramic additives have been introduced into the polyethylene. These mixtures have however proved difficult to work compared with those containing only polyethylene.
Furthermore, in conveyors comprising several side-by-side curved elements, or in conveyors comprising several side-by-side chains, for reasons of modularity it has been considered to use the same number of magnets for the more outer curved elements, ie those of greater radius, as for the more inner elements. It has however been found experimentally that particularly at high speeds it can happen that the more outer chains do not always remain adhering to the relative rails.